The present invention relates to the adhesive securing of an object in a hole. More particularly this invention concerns a cartridge which contains both components of a two-component adhesive used to secure the end of an extensometer, rock bolt or the like in a mine borehole.
It is known to secure a borehole anchor such as described in the commonly assigned patent application Ser. No. 666,633 filed Mar. 15, 1976 or an extensometer such as described in the commonly assigned and copending patent application Ser. No. 582,417 filed May 29, 1975 in a mine borehole by means of an adhesive cartridge. The cartridge is placed at the blind end of the hole and the object being anchored in the hole is then inserted into the hole so as to break this cartridge and mix together the two components, usually hardener and resin of an epoxy-type adhesive, so that they react and form an extremely strong bond between the object being secured and the borehole. To this end the inner end of the object being secured is normally provided with a pointed mixing tip that serves to break the cartridge and which, on rotation, serves to mix together the two components of the adhesive.
In the commonest such cartridge there is provided an outer glass envelope which contains the resin and a filler. Also received within this outer glass envelope is a smaller inner glass envelope in which the hardener is contained. Thus the hardener, i.e. a curing agent, and the resin are kept separate, but breaking of the highly fragible glass envelope allows the two components to be mixed together and react.
It is also known to eliminate the inner envelope and imbed the hardener as a bar or solid granules in the mass of resin.
The obvious difficulty with such a cartridge is that during transport or at any time prior to use it is relatively easy to break the outer glass envelope, whereupon the cartridge becomes useless. Furthermore, the glass splinters present a considerable potential for injury to the persons handling the cartridge, and the resin can present further chemical burn hazards.
It has been suggested in recent times to inject the cartridge into the borehole by use of an elongated tube which is inserted into the borehole and pressurized in back of a cartridge so as effectively to "shoot" the cartridge into the end of the borehole. Since the typical glass cartridge is between 50 mm and 1000 mm long and has a wall thickness of between 0.3 mm and 0.8 mm, it is impossible to use this glass cartridge in an arrangement of this type wherein the insertion tube must inevitably bend somewhat.
It has further been suggested to provide an adhesive cartridge of the above-described general type wherein the outer envelope is formed of a synthetic-resin foil. This outer envelope is formed as a tube of a polymer. The hardener is either provided in a separate synthetic-resin tube inside the outer tube, or the outer tube is simply partitioned into two compartments, one of which contains the hardener and the other the resin. In both cases the two components are separated by a polymer partition wall. The main disadvantage of such an arrangement is that it is relatively limp so that slipping it into the borehole is a difficult operation. Thus, it is standard practice to provide a stiffening tube around such a cartridge in order to allow it to be slid into the bore with ease. Such an arrangement, however, has the considerable disadvantage that quite a bit of synthetic-resin foil is left in the borehole so that the adhesive cannot form a good bond with the wall of the borehole, as typically the adhesive remains mostly inside the stiffening tube even after breaking of the two envelopes. This disadvantage can be at least partially overcome by providing one of the components in a glass tube inside the synthetic-resin envelope of the other component. Thus the broken tube forms glass splinters that will shred and pierce the envelope and stiffening tube so as to form a good bond between the adhesive and the walls of the borehole. Such use of a glass envelope, however, has all the disadvantages of the glass-type cartridges.
It has also been suggested to form the outer envelope out of a polyamide foil. The hardener is once again provided in a glass capsule or envelope inside the polyamide outer sleeve. Once again this cartridge has the disadvantage that if the central glass envelope is broken during transport or handling the outer envelope will be pierced. Thus the contents can leak out so that the above-mentioned disadvantages of injury, chemical burn, and the like are all present.
All of the synthetic-resin cartridges using synthetic-resin tubes of foil have in addition the disadvantage that when used with an unsaturated polyester resin as the hardener it is possible for styrene to diffuse through the foil outwardly. This causes the cartridge to lose its stiffness and to expose the persons handling the unused cartridge to styrene fumes. Storage of large quantities of such cartridges creates a potentially explosive mixture of styrene and air.
Both the synthetic-resin cartridges and the glass cartridges are usually transparent to ultra-violet light. This greatly decreases the shelf life of the cartridges, since the ultraviolet radiation triggers polymerization in an unsaturated polyester resin. Thus, when the time comes to use the adhesive cartridge there is very little reactable resin left, so that a poor bond is formed between the rock anchor or the like and the borehole.